1. Field of the Invention
The present invention relates generally to the field of drug delivery systems. In particular, the present invention relates to osmotic pump systems.
2. Description of the Related Art
Since the beginning of modern medicine, drugs have been administered orally. Patients have taken pills as recommended by their physician. The pills must pass through the digestive system and then the liver before they reach their intended delivery site (e.g., the vascular system). The actions of the digestive tract and the liver often reduce the efficacy of medication; furthermore, medications delivered systemically sometimes cause undesirable side effects. Over the course of the past few decades, drug delivery technology and administration has evolved from oral delivery to site-specific delivery. In addition to the oral route of administration, drugs are also routinely administered via the vascular system (intravenous or IV). Intravenous drug delivery has the advantage of bypassing the acidic and enzymatic action of the digestive system. Unfortunately, IV administration requires the use of a percutaneous catheter or needle to deliver the drug to the vein. The percutaneous site requires extra cleanliness and maintenance to minimize the risk of infection. Infection is such a significant risk that IV administration is often limited to a number of weeks, at most. In addition, the patient must wear an external pump connected to the percutaneous catheter.
The next step in the evolution of drug delivery was the implanted pump. The implanted pump is a device that is completely implanted under the skin of a patient, thereby negating the need for a percutaneous catheter. These implanted pumps provide the patient with a drug at a constant or a programmed delivery rate. Constant rate or programmable rate pumps are based on either phase-change or peristaltic technology. When a constant, unchanging delivery rate is required, a constant-rate pump is well suited for long-term implanted drug delivery. If changes to the infusion rate are expected, a programmable pump may be used in place of the constant rate pump. Fully implanted constant rate and programmable rate infusion pumps have been sold in the United States for human use since the late 1970s and early 1980s, respectively. Two problems associated with such 1970s and 1980s vintage constant rate and programmable rate infusion pumps relate to their size and their cost. Current implantable constant rate and programmable pumps are about the size and shape of hockey pucks, and they typically are sold to the hospital for $5,000-$9,000. The current implantable pumps must be implanted in the Operating Room under general anesthesia, which further increases costs, as well as the risk, and discomfort to the patient. The size and cost of such pumps has proven to be a substantial barrier to their use, and they are rarely used to deliver medication. An added drawback of phase-change and peristaltic pumps is that they must be refilled with drug every 3-8 weeks. Refills constitute an added burden to the caregiver, and add further costs to an already overburdened healthcare system. The burden associated with such refills, therefore, further limits the use of phase-change and peristaltic pumps.
In the 1970s, a new approach toward implanted pump design was commercialized for animal use only. The driving force of the pumps based upon this new approach utilized the principle of osmosis. Osmotic pumps may be much smaller than other constant rate or programmable pumps, because their infusion rate can be very low. A recent example of such a pump is described listed in U.S. Pat. No. 5,728,396. This patent discloses an implantable osmotic pump that achieves a sustained delivery of leuprolide. The pump includes a cylindrical impermeable reservoir that is divided into a water-swellable agent chamber and a drug chamber, the two chambers being divided by a movable piston. Fluid from the body is imbibed through a semi permeable membrane into the water-swellable agent chamber. As the water-swellable agent in the water-swellable agent chamber expands in volume, it pushes on the movable piston, which correspondingly decreases the volume of the drug chamber and causes the drug to be released through a diffusion outlet at a substantially constant rate.
The aspect ratio of such cylindrical osmotic pump delivery devices is large, and often not compatible with the human body. Indeed, the human body does not have naturally-formed cylindrical cavities in which to implant such devices in the patient, in an unobtrusive and comfortable manner. The principal reason for the cylindrical designs of conventional osmotic pump drug delivery systems is that they rely upon a movable piston design to push out a volume of drug from the drug chamber as the osmotic water-swellable agent expands. Pistons, however, must be cylindrical to avoid binding the pump housing as the piston moves. This problem is exacerbated by the fact that the water-swellable agent within the water-swellable agent compartment often does not expand evenly, which may exert localized increased pressure on the piston, causing the piston to bind within the pump housing. In turn, this binding may affect the delivery rate of the device and reduce the therapeutic benefits of the implantable pump.
What are needed, therefore, are non-cylindrical implantable osmotic pumps. What are also needed are implantable osmotic pumps that conform to the patient""s anatomy and that more closely match the topology of the implant site. Also needed are novel implantable osmotic pump designs that do not rely upon a piston to infuse a drug or drugs into the patient.
It is an object of the present invention, therefore, to provide non-cylindrical implantable osmotic pumps. It is also an object of the present invention to provide implantable osmotic pumps that conform to the patient""s anatomy and that more closely match the topology of the implant site. Another object of the present invention is to provide novel implantable osmotic pump designs that do not rely upon a piston to infuse a drug or drugs into the patient.
In accordance with the above-described objects and those that will be mentioned and will become apparent below, an implantable osmotic pump system, according to an embodiment of the present invention, includes a rigid pump housing defining an opening; at least one membrane assembly fitted to the pump housing; an osmotic engine within the rigid pump housing, and a flexible pharmaceutical agent compartment disposed within the rigid pump housing, the flexible pharmaceutical agent compartment being in fluid communication with the opening.
According to further embodiments, the membrane assembly may include a semipermeable membrane and may include an impermeable membrane initially sealing the semipermeable membrane, the impermeable membrane being adapted to be breached by a lancet. The impermeable membrane may be disposed away from the semipermeable membrane to define a fluid tight compartment therewith, which compartment may enclose a volume of saturated saline solution. The impermeable membrane may include a biologically inert material that is impermeable to water and that may be radiopaque. The impermeable membrane may include titanium, steel, polyethylene, polyethylene teraphthalate (PET), PETG and/or PETE. The impermeable membrane may include or be coated with a layer of gold, silver, platinum and/or platinum-iridium, for example.
The osmotic engine may include a xe2x80x9cconventionalxe2x80x9d osmotic engine. Instead of a xe2x80x9csalt blockxe2x80x9d, the osmotic engine may include a xe2x80x9csalt waferxe2x80x9d. The osmotic engine may be a hygroscopic salt and/or may include an absorbent polymer. The absorbent polymer may include a material selected from a group including poly(acrylic acid), potassium salt; poly(acrylic acid), sodium salt; poly(acrylic acid-co-acrylamide), potassium salt; poly(acrylic acid), sodium salt-graft-poly(ethylene oxide); poly (2-hydroxethyl methacrylate); poly(2-hydroxypropyl methacrylate) and poly(isobutylene-co-maleic acid) or derivatives thereof.
The pharmaceutical agent may be therapeutically effective for pain therapy, hormone therapy, gene therapy, angiogenic therapy, anti-tumor therapy, chemotherapy and/or other pharmaceutical therapies. For example, the pharmaceutical agent may include an opioid. The pharmaceutical agent may include an agonist, a partial agonist, an agonist-antagonist and/or an alpha 2-adrenoreceptor agonist, for example. According to further embodiments, the pharmaceutical agent may include one or more of the following drugs: morphine, hydromorphone, levorphanol, methadone, fentanyl, sufentanil, buprenorphine, pentazocine, butorphanol or the like.
The flexible pharmaceutical agent compartment may be made of or include a substantially impermeable material and may include polyethylene, PET, PETG and/or PETE and may be laminated with gold, silver, platinum, aluminum or other metal(s) to increase impermeability to gases and liquids. A catheter may be bonded to the opening of the pump housing and to a corresponding opening in the flexible pharmaceutical agent compartment so as to define a fluid path from the flexible pharmaceutical agent compartment through the opening of the pump housing to the catheter. According to one embodiment, the flexible pharmaceutical agent compartment may be free floating inside the pump housing and may be attached only to the catheter and/or the opening of the pump housing. The pump housing may have a non-cylindrical shape and/or may have a shape that conforms to a patient anatomy at an implantation site.
The pump housing may include a proximal end, a distal end and a sidewall, and one or more membrane assemblies may be fitted to the sidewall. The membrane assembly or assemblies may include an array of membrane assemblies, each of which may include a semipermeable membrane initially sealed by a radiopaque impermeable membrane adapted to be breached with a lancet.
The present invention is also an implantable osmotic pump, comprising a pump housing; an osmotic engine, the osmotic engine being disposed within the pump housing; a semipermeable membrane, the semipermeable membrane being configured to allow water to cross from a patient into the pump housing to the osmotic engine, and a flexible pharmaceutical agent compartment adapted to enclose a volume of pharmaceutical agent.
The flexible pharmaceutical agent compartment may be adapted to infuse the volume of pharmaceutical agent at a selected infusion rate as the osmotic engine hydrates and swells with the water from the patient, the selected infusion rate being related to the thickness, the composition and/or the surface area of the semipermeable membrane or to the sum of the individual contributions of the thickness, composition and surface area of the semipermeable membrane. The pump housing may include a proximal end, a distal end and a sidewall, and the semipermeable membrane may be fitted to the sidewall. The pump housing may include a proximal end, a distal end and a sidewall, and the semipermeable membrane may be fitted to the proximal end. A plurality of semipermeable membranes may be provided, each being adapted to allow water to cross into the osmotic engine. Each of the plurality of semipermeable membranes may be fitted with an impermeable membrane that initially seals the semipermeable membrane. The impermeable membrane may radiopaque. The osmotic engine may be at least co-extensive with the flexible pharmaceutical agent compartment. The pump housing may be cylindrical or may have a non-cylindrical shape.
The pharmaceutical agent may be therapeutically effective for pain therapy, hormone therapy, gene therapy, angiogenic therapy, anti-tumor therapy, chemotherapy and/or other pharmaceutical therapies. The pharmaceutical agent may include an opioid and/or may include an agonist, a partial agonist, an agonist-antagonist and/or an alpha 2-adrenoreceptor agonist. For example, the pharmaceutical agent may include one or more of the following drugs: morphine, hydromorphone, levorphanol, methadone, fentanyl, sufentanil, buprenorphine, pentazocine, butorphanol or the like.